Some applications of speech processing require repeatable transduction of speech frequencies and a full range of speech volume. One such application is speech recognition. Another is speech compression (for applications such as "voice mail"). As such, methods for positioning microphones are needed to optimize acoustic performance of microphones for speech signal reception.
In order to receive consistent frequency response from a user, the microphone must be placed in a fixed position relative to the acoustic source, i.e. the mouth, the nose, etc. This eliminates methods using microphones fixed to position that is external to the sound source; for example, on a desk, boom, gooseneck, or lapel. Prior art methods to provide a fixed microphone position, relative to the source, have included throat microphones, head gear with a microphone extension (fixed or adjustable), and helmets with microphone elements fitted to the interior.
For some applications, prepositioned or adjustable headgear microphones such as the Shure SM-10 (U.S. Pat. No. 4,039,765) may be adequate. However, for voice recognition applications, consistent placement is not assured each time the speaker mounts the headgear. A second prior art solution proposed includes use of a microphone boom with a fitted ear clip; but as there is freedom of movement from 5-15 degrees, the microphone boom cannot be consistently positioned. Neither approach is convenient for usage in an office environment which may involve frequent removal of the microphone to leave the office, answer the telephone, etc.
Additionally, helmet mounted microphones require measurements of each user's head for proper size, mounting, and alignment. The helmet's weight and inconvenienee limits its general acceptability.
Other prior art devices include throat microphones (see, U.S. Pat. No. 2,340,777) which provide a fixed reference location. However, throat microphones do not provide clear reception of acoustic signals produced by articulations of the tongue, teeth or lips, nor is there any useful reception of nasal sounds.